FIG. 1 is a block diagram of a network structure of a mobile communication system of UMTS (universal mobile telecommunications system).
Referring to FIG. 1, a UMTS mainly consists of a user equipment (UE), a UMTS terrestrial radio access network (hereinafter abbreviated UTRAN), and a core network (hereinafter abbreviated CN).
The UTRAN consists of at least one radio network subsystem (hereinafter abbreviated RNS). Each RNS consists of one radio network controller (hereinafter abbreviated RNC) and at least one base station (hereinafter named Node B) managed by the RNC. A MAC-e sublayer or similar-entity may be provided according to a controlled transport channel type.
FIG. 2 is a structural diagram of a radio interface protocol between UE and UTRAN (UMTS terrestrial radio access network) based on the 3GPP radio access network standard.
Referring to FIG. 2, a radio interface protocol horizontally consists of a physical layer, a data link layer, and a network layer and vertically consists of a user plane for data information transfer and a control plane for signaling transfer.
Protocol layers in FIG. 2 can be divided into a first layer (L1) a second layer (L2) and a third layer (L3) based on three lower layers of the OSI (open system interconnection) standard model widely known in communication systems.
The physical layer of the first layer provides an information transfer service to higher layers using a physical channel. The physical layer is connected to a medium access control layer above the physical layer via a transport channel. Data are transferred between the medium access control layer and the physical layer via the transport channel. And, data are transferred between different physical layers, i.e., the physical layer of a transmitting side and the other physical layer of a receiving side via the physical channel.
The medium access control (hereinafter abbreviated MAC) layer of the second layer provides a service to a radio link control layer above the MAC layer via a logical channel. And, the MAC layer is divided into various kinds of sublayers including a MAC-d sublayer, a MAC-e sublayer and the like according to a controlled transport channel type.
Structures of DCH (dedicated channel) and E-DCH (enhanced dedicated channel) are explained as follows.
DCH and E-DCH are transport channels dedicated to one user equipment. In particular, E-DCH is used for the user equipment to transfer uplink data to UTRAN and is capable of transferring the uplink data faster than DCH. To transfer data fast, E-DCH employs HARQ (hybrid ARQ), AMC (adaptive modulation and coding), Node B controlled scheduling and the like.
For E-DCH, Node B transfers downlink control information to UE to control E-DCH transfer of the UE. The downlink control information includes response information (ACK/NACK), E-DCH resource allocation information for Node B controlled scheduling and the like. Meanwhile, UE transfers uplink control information to Node B. The uplink control information includes E-DCH resource allocation request information (rate request information) for Node B controlled scheduling, UE buffer status information, UE power status information and the like.
MAC-d flow is defined between MAC-d and MAC-e for E-DCH. A dedicated logical channel is mapped to MAC-d flow, MAC-d flow is mapped to the transport channel E-DCH, and the transport channel E-DCH is mapped to a physical channel E-DPDCH (enhanced dedicated physical data channel) again.
The MAC-d sublayer is in charge of managing DCH (dedicated channel) dedicated to a specific UE. And, MAC-e/MAC-es sublayer is in charge of a transport channel E-DCH (enhanced dedicated channel) used in transferring fast uplink data.
A transmitting side MAC-d sublayer configures MAC-d PDU (protocol data units) from MAC-d SDU (service data units) delivered from a higher layer, such as the RLC layer. A receiving side sublayer plays a role in restoring MAC-d SDU from the MAC-d PDU received from a lower layer to deliver to a higher layer. In doing so, the MAC-d sublayer mutually exchanges the MAC-e sublayer with the MAC-d PDU or a physical layer with MAC-d PDU over DCH. The receiving side MAC-d sublayer restores MAC-d SDU for delivery to a higher layer using a MAC-d header included in the MAC-d PDU.
A transmitting side MAC-e/MAC-es sublayer configures MAC-e PDU from MAC-d PDU delivered from a higher layer, such as a MAC-d sublayer. A receiving side MAC-e sublayer plays a role in restoring MAC-es PDU from the MAC-e PDU received from a lower layer, such as a physical layer. A receiving side MAC-es sublayer plays a role in restoring MAC-d PDU from MAC-es PDU for delivery to the MAC-d sublayer. In doing so, the MAC-e sublayer exchanges the physical layer with MAC-e PDU via E-DCH.
FIG. 3 is a diagram of a protocol for E-DCH.
Referring to FIG. 3, a MAC-e sublayer supporting E-DCH exists below each MAC-d sublayer of UTRAN and UE. The MAC-e sublayer of the UTRAN is located at Node B and the MAC-e sublayer exists in each UE.
Meanwhile, a MAC-d sublayer of the UTRAN is located at SRNC in charge of managing the corresponding UE. And, the MAC-d sublayer exists in each UE.
Control information transmission over E-DCH is explained as follows.
In E-DCH, a scheduler exists in the Node B. The scheduler plays a role in allocating optimal radio resources to UEs located within one cell to raise transmission efficiency of data arriving at the Node B from the entire UEs within each cell in the uplink direction, respectively. Specifically, in one cell, a UE in good radio channel status can transmit more data by receiving more radio resource allocation, whereas another UE in poor radio channel status is prevented from transmitting interference signals over an uplink radio channel by receiving less radio resource allocation. Hence, a quantity of uplink data transmissions in the entire cell can be optimized in the above-explained manner.
Yet, the scheduler considers other factors as well as the radio channel status of the UE in allocating radio resources to the UE. The scheduler needs control information from UEs. For example, the control information includes a power that can be used for EDCH by the UE, a quantity of data the UE attempts to transmit, and the like. In other words, although the UE is in excellent radio channel status, if there is no spare power the UE can use for the E-DCH or if there is no data the UE will transmit in uplink direction, it is not allowed to allocate the radio resources to the UE. Hence, the scheduler just allocates the radio resources to the UE having the spare power for the E-DCH and the data to transmit in uplink, thereby raising efficiency in using the radio resources within one cell.
So, the UE has to send control information to the scheduler at the Node B in various ways. For instance, the scheduler at the Node B can order the corresponding UE to report if the data to be transmitted in uplink exceeds a predetermined value or the Node B can order the UE to send the control information to the Node B itself periodically.
The UE, to which the radio resource was allocated, configures MAC-e PDU within the allocated radio resource and then transmits the MAC-e PDU to the Node B over E-DCH.
Namely, the UE having the data to be transmitted sends the control information to the Node B to notify that there is the data to be transmitted by the UE itself. The scheduler of the Node then sends the information indicating the allocation of radio resource to the UE based on the control information having sent from the UE. In this case, the information indicating the allocation of radio resource means a maximum power for uplink transmission from the UE, a ratio to a reference channel, etc. The UE configures MAC-e PDU within the allowed range based on the information indicating the allocation of the radio resource and then transmits the configured MAC-e PDU.
In brief, in the E-DCH, incase of having data to be transmitted, the UE informs the Node B that there is the data to be transmitted. Once the radio resource is allocated to the UE from the Node B, the corresponding UE transmits real user data in a direction of the Node B.
In this case, a size of the radio resource is named a radio resource allocation quantity, which means a maximum value of power allowed to the UE to use and the like in case that the UE transmits the data in uplink. IF there is no radio resource allocation quantity and if there exists the data to be sent in uplink, the UE sends radio resource allocation request information to the Node B. Once receiving a radio resource allocation message from the Node B, the UE transmits the data in uplink using the power within a radio resource allocation quantity range indicated by the message.
If there is the radio resource allocated to the UE, i.e., if the radio resource allocation quantity is not zero (there is data to be transmitted in uplink), the corresponding UE immediately transmits the data in the uplink.
As mentioned in the foregoing description, in order for the UE to transmit the user data in uplink, it is important for the UE to transmit the appropriate radio resource allocation request information to the Node B at the proper time to have a suitable radio resource allocation quantity set by the Node B. The appropriate radio resource allocation quantity is important, which is because the allowable radio resource in the mobile communication system is limited.
However, the above-explained related art method has the following problem.
For instance, assuming that the power usable for uplink transmission of the UE is 10 dBm, if the quantity of the radio resource allocated to the UE is 20 dBm, this means a waste of the radio resource. If the power acceptable by the cell is 20 dBm, another UE loses its chance to transmit data in uplink.
Hence, the demand for a method of allocating a radio resource most efficiently within a radius of one Node B rises.